The National Institute of IT and Communication Technology (NICT) in Japan has been diligently working for many years on dramatically increasing fibre optic bandwidth by using a wider spectrum range than the traditional C and L bands. The long haul fibre optic networks have relied exclusively on the C and L bands because they offer the lowest optical attenuation for silicon-based fibre optics. Light in these frequency bands fades and loses strength relatively slowly as it passes through fibre optic glass. But as the chart below shows, the C and L bands comprise just a fraction of the available spectrum that lasers can use.
In this trial the NICT achieved 450 Tbps on a repeatered London metro fibre pair connecting Telehouse London to the University of London. Because existing optical amplifiers are designed to work only in the C and L bands, NICT has spent years developing amplifiers optimized for the O, E, S, and U bands. These bands required that the fibre optic strands in the amplifier be doped with materials other than the rare metal erbium used for the C and L bands. In addition, there is the issue of repeater distance. Since frequencies like the S band lose optical power faster than the C or L bands, adjustments may be required in amplifier spacing or amplifier power. Today there are no commercial products tailored to these bands for long haul transport. All these factors have held back commercial adoption. NICT sees its role as doing the fundamental R&D that will pave the way to higher transmission rates.
